A student standing on a longboard begins at rest on a level sidewalk
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A student standing on a longboard begins at rest on a level sidewalk, pushes off, coasts, and then drags a foot to slow down and reverse direction. The motion can be divided into three consecutive time intervals:
• Interval I (push-off): From t=0s to t=2s, the board’s speed increases steadily until it reaches 3.0ms−1 in the forward direction.
• Interval II (coast): From t=2s to t=7s, the board moves at constant speed.
• Interval III (braking): From t=7s to t=10s, the board slows uniformly until it is moving 1.0ms−1 in the opposite (rearward) direction.
(a) For each of the three intervals, describe the sign (positive, zero, or negative) and relative magnitude of the board’s average acceleration. Provide reasoning based on how the velocity changes during each interval.
(b) Comparing Interval I and Interval III, explain which interval involves the greater magnitude of average acceleration and justify your answer without performing any formal calculations.
(c) Sketch a qualitative graph of velocity versus time for the entire 0–10s period. On your sketch, indicate the slope in each interval and show how your description of average acceleration from parts (a) and (b) corresponds to the slope.